Engine out on the YZF-R125

The first step towards getting my beloved R125 running again is going to be taking the engine out to see what went wrong and whether I can fix it or whether I have to replace it.

If there’s any way I can fix the motor then I’m going to try and do that, and possibly slip a 180cc big bore kit in there too since I probably have to replace the cylinder anyway and my very patient insurance folks have said they will insure it if I go ahead.

If it doesn’t work I can still order a drop-in replacement motor. The only real loss/cost would be what I’ve spent on parts (if I can’t get it to run) which would be annoying but not the end of the world, and if it works…well then \o/… so let’s see how far we get.

Whilst I’ve done a couple of reasonably in-depth videos recently (clutch change, cam chain tensioner etc) I think this might be where we’re getting into some deeper water and I start to be at the limits of my knowledge and xp.

I know I’m feeling kinda nervous about the process because I want to get it right. I am by _no means_ an “engine builder” however, I have in the past built a couple of engines for my old VW golfs, replaced a few cylinder heads etc after various meltdowns (generally from DLAC).

I used to get that same slight panic feeling then as I have now about having the guts of my baby so very in bits on the driveway…no way back, already committed for parts etc (usually in November/freak-snow too ofc).

But much to everyone’s (including my) surprise those engines actually ALL ran and ran well…and they were about 4x larger and more complicated than this little motor, and I’ve learnt a lot since then too…so *hopefully*, with a bit of luck, I just need to stay on target, be methodical, stick to what I know, follow the steps and she’ll be back better than ever at which point i will be back out there learning how to rip dank nooners, or even just deeply appreciative to having a working bike again and super-gently running her in for the appropriate thousand km. Fingers crossed!

The job took about 5 hours, working at a pretty relaxed pace with little breaks here and there. the video is speeded up 4x.

DISCLAIMER: As usual, this is not a “how to” video, the way I’ve done things may or may not be the best way. The idea here is just to kinda show what sort of thing is involved in case you’re thinking about doing something similar, or just interested in how these machines look on the inside.


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